1. Field of the Invention
This invention relates generally to pistons and methods of construction thereof, and more particularly to piston mold assemblies and pistons molded therewith.
2. Related Art
It is known to construct a piston with an annular cooling gallery having an external undercut located immediately radially inward of a piston ring belt. The undercut provides an overhanging portion of ring belt, which in turn causes problems in casting of the piston. To avoid machining the undercut after casting, the mold cavity must have a projection or panel with a negative shape of the desired undercut. However, in order to extract or remove the molded piston from the mold cavity, the panel must be moved completely out of the undercut and the mold cavity. Because the depending ring belt is formed radially outward from the undercut, the panel cannot be simply moved radially outwardly in a purely horizontal direction. Additionally, pin bosses depending from the ring belt are formed in the molding process. The pin bosses are spaced from one another and flare laterally outwardly with respect to a central axis of the piston. As such, the pin bosses prevent the undercut forming panel from being moved downwardly in a purely vertical direction. Accordingly, to overcome this problem, known mold assemblies include a panel that must be pivoted out of the mold cavity. However, the pivoting motion of the panel restricts the size of the available undercut that can be formed depending on the envelop dimensions of the mold cavity.